The present invention generally refers to an adjustment mechanism, and more particularly is directed to an adjustment mechanism of a type having two structural elements moveable relative to one another, with the first structural element being formed with at least one row of substantially cycloidal teeth, and with a second structural element including a drive element guided transversely to a direction of adjustment and formed with at least two driving pins capable of rolling over the teeth. Moreover, the present invention refers to an operating device for activating the adjustment mechanism, and in particular to an operating device in the form of a handle, such as a crank.
Such adjustment mechanisms are typically used for moving and adjusting structural elements of different kinds that do not require a continuous control but are adjusted step-by-step for dispositions in especially evenly distributed, predetermined increments, i.e. operate as a stepping drive. These types of adjustment mechanisms are typically used to allow the user to suit the structural elements such as desks, chairs, armrests and backrests, platforms and the like, or other typically hand-operated gearings such as window lifters, sun shades, winches or rope winches, clamping devices etc., to his or her height and to lock the selected position.
Evidently, it is advantageous when the user is afforded the possibility to recognize or sense the locked positions during manual adjustment in order to enable a counting of required incremental steps and to eliminate, by resorting to mechanical locks, the risk that the adjustment mechanism shifts by itself when being fixed in these locked positions. Further, adjustment mechanisms are demanded that are so designed as to overcome a counterforce such as gravitational forces, weight, rope pull force or spring force, and to allow an adjustment in both directions, without necessitating a trigger of a back-run safety devices such as ratchets, or a release of brakes. Moreover, adjustment mechanism of the type involved here should be of simple construction, allow cost-efficient production, is easy to operate, permits manual or motor-driven operation, preferably with (detachable) crank, whereby the rotational direction determines the direction of adjustment, and attains a safe operation, without posing a risk for the operator. Finally, the adjustment mechanism should be of overall small size but yet display a high load-carrying capability. In particular, adjustment mechanisms of this type should be free from play for most applications, e.g. for desks.
Adjustment mechanisms of this type have been known for a long time. It is known e.g. to provide an adjustment mechanism in the form of a pin gearing, with a pinion engaging a rack having two driving pins. The distance between two locked positions equals the distance between the driving pins and corresponds to a rotation of the pinion by 180.degree.. In each locked position, the pinion is secured in place because a displacement of the rack will not cause a rotation of the pinion. These types of adjustment mechanisms have however the drawback that the driving pins can not be subject to high loads because a high rolling pressure is encountered between the relatively small driving pins and the tooth flank, and the lever arm between the contact point of the driving pin and the bottom land of the tooth is relatively long.
Frequently, the use of a overhung-mounted pinion is proposed which is pressed against the rack by a spring force in order to secure the pinion relative to the rack and to ensure that at least one driving pin bears upon the bottom land to substantially increase the load-carrying capability. These types of adjustment mechanisms have, however, the drawback that an overload may cause frictional forces to overcome the spring force so that the driving pins may become at least partially disengaged from the teeth or both driving pins may only bear upon the tooth peaks, resulting in possible damage of the teeth. A substitution of the spring to effect a secure constraint of the pinion can be effected only by resorting to highly complex measures which run counter to the desired simplicity of the adjustment mechanisms. Thus, conventional adjustment mechanisms can be used only at small forces in risk-free areas.
It is also known to use a so called Geneva mechanism in which a pinion is provided with only a single driving pin. This mechanism can not be subjected to high loads and exhibits a particularly long dead travel equaling to about a 3/4 revolution of the pinion, without effecting any adjusting action.